Environ. Sci. Technol. 1999, 33, 369-370
Comment on “Identification of Estrogenic Chemicals in STW Effluent. 1. Chemical Fractionation and in Vitro Biological Screening”
to 1/3 less than the quoted value. Further research on the Naburn STW showed that much of the population equivalents were generated by industrial customers. The calculation was then made on real head of population served by this STW using new information.
SIR: A recent paper by Desbrow and co-workers demonstrated the presence of steroid estrogens in sewage effluent in the U.K. (1). It is of great interest to know how efficiently the sewage treatment works (STW) are removing these compounds from the influent. In the absence of data on influent concentrations we believe some estimates can be made using the STW data given in the paper. We did this for estradiol (E2) and biased our calculations to give the maximum possible influent concentrations in each case. To start the calculation a number of assumptions were made.
From these calculations there was no evidence that the activated sludge systems were more efficient than the biological filter systems, despite the hydraulic residence time of the former being more than double the latter (14 h compared to 5 h). If biodegradation was the most important process in preventing escape of E2 it might have been expected that the activated sludge STW would have had an advantage over the biological filter STW. While from the E2 data there was no evidence that the activated sludge STWs had better performance than the biological filter STW, this was contradicted by the ethynylestradiol (EE2) data. Here Desbrow et al. (1) showed that the biological filter STWs leaked EE2, whereas the activated sludge plants did not. However, the EE2 values were at the edge of the detection limit so perhaps we should not infer too much at this stage.
Population equivalents actually represent head of population (an overestimate). The population is split 50:50 male: female. Although E2 is excreted as a conjugate, deconjugation is complete when the hormones arrive at the STW. Half the population are male, and they all excrete 1.6 µg/day E2 (2). Sixty percent of the female population are menstrual (assumption taken from the 1991 census for Oxfordshire, for women between ages of 15-59), and they excrete 3.5 µg/day E2 (slight overestimate, 2). One in 75 females are pregnant (based on no. births in Oxford vs population) and they excrete 259 µg/day E2 (value for later stages of pregnancy, 2). The effluent flow in a STW is constant. The influent E2 concentration is constant. Other estrogens such as estriol, 16epiestriol, or 16-oxoestradiol are not converted to E2 in the sewers. Thus, for Harpenden STW, a percolating filter, sampled in summer, it has a 31 200 population; of these we assume 15 600 males are excreting 25 mg/day E2. There are 9360 menstrual females excreting 33 mg/day E2. There are 208 pregnant females excreting 54 mg/day E2. This gives a total of 112 mg/day E2 entering the STW in 8.25 × 106 L/day of water, giving 13.6 ng/L/day E2 in the influent. The quoted effluent values (1) were 3.7-7.1 ng/L. Therefore, the STW removed only 48-73% of the E2 from the influent. The same calculation was done for the other STW described in the Desbrow et al. (1) paper. Southend STW was not included, its calculated maximum input was 17 ng/L E2 yet its effluent concentrations ranged from 29 to 48 ng/L, 170 or 282% of the original! It is hard to explain the discrepancy unless the mean daily flow was 1/2
Our own lab data (3) on the potential of organic flocs to sorb E2 from the R. Calder (Yorkshire, U.K.) gave an equilibrium distribution coefficient (Kd) value of 3360 L/kg following a 22 h equilibration. The samples collected from the R. Calder came from a very urban/industrial stretch of the river. If we assume the flocs in a activated sewage plant have the same properties, then a calculation can be made on the amount of E2 which could be sorbed. The quantity of floc particles in an activated sludge plant is around 3.5 g/L; therefore, this quantity over 22 h would be expected to sorb 92% of the E2 present in the water. Thus, ignoring degradation, 92% removal of E2 might be expected from the activated sludge plants. The best removal value we estimated was 81% (Rye Meads), residence time in this type of STW is more like 14 h than 22 h, which may help to explain the discrepancy (although the kinetics would be expected to be fast). While much can be done to refine these calculations, our estimates are not far from estimated values of removal quoted by other researchers: 50-70% removal in the U.S.A. (4), 5891% removal of steroids in German STWs (5), and 80% removal of estrogens in Israeli STW (6). These calculations suggest that there is room for improvement in STW performance if we wish to make significant reductions in the estrogen content of sewage effluent.
TABLE 1. Estimated E2 Removal by STWs
type
season
location
water consumption per head
percolating filter biological filter biological filter extended aeration activated sludge activated sludge
summer winter winter winter summer summer
Harpenden Horsham Naburn Billing Deephams Rye Meads
264 l 167 l 151 l 210 l 201 l 248 l
10.1021/es9809197 CCC: $18.00 Published on Web 12/08/1998
1999 American Chemical Society
estimated E2 input (ng/L) 13.6 21.3 24 17 17.8 14.4
measured E2 output (ng/L) Desbrow et al. (1) 3.7-7.1 4-5.7 6.5-10 6.1-7.4 4.3-12 2.7-6.3
percentage removal 48-73 73-81 58-73 57-64 33-76 56-81
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Literature Cited (1) Desbrow, C.; Routledge, E. J.; Brighty, G. C.; Sumpter, J. P.; Waldock, M. J. Environ. Sci. Technol. 1998, 32, 1549-1558. (2) Fotsis, T.; Aldercreutz, H. J. Steroid Biochem. 1987, 28, 203213. (3) Ju ¨ rgens, M. D.; Williams, R. J.; Johnson, A. C. R&D Technical Report P161 for Environment Agency, UK. (4) Tabak, H. H.; Bloomhuff, R. N.; Bunch, R. L. Dev. Indus. Micro. 1981, 22, 497-519. (5) Stumpf, M.; Ternes, T. A.; Haberer, K.; Baumann, W. Vom Wasser 1996, 87, 251-261. (6) Shore, L. S.; Gurewitz, M.; Shernesh, M. Bull. Environ. Contam. Toxicol. 1993, 51, 361-366.
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Andrew C. Johnson* and Richard J. Williams Institute of Hydrology, Wallingford Oxfordshire OX10 8BB, UK
Thomas Ulahannan Endocrinology Department Radcliffe Infirmary, Oxford, UK ES9809197
